Spectroscopic properties of aromatic dicarboximides part 4: N-alkyl- and N-cycloalkyl-substituted 1,2-naphthalimides

P. Nemes, A. Demeter, L. Biczók, T. Bérces, V. Wintgens, P. Valat, J. Kossanyi

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Abstract

The photophysics of a series of N-alkyl- and N-cycloalkyl-substituted 1,2-naphthalimides has been investigated. Fluorescence spectra, fluorescence quantum yields and decay times as well as triplet yields are determined in a wide temperature range. The rate coefficients for fluorescence are independent of temperature. However, she rate of non-radiative processes shows characteristic temperature dependence, consisting of a temperature independent and a temperature-dependent component: Knr = k°nr + knrT = k°nr+ Anr exp( - Enr/RT), where nr designates either intersystem crossing or internal conversion. The temperature-independent component of internal conversion can be associated with a direct process in which the electronic energy is dissipated by a single mode, probably an aromatic vibrational mode. Vibrational coupling between the two lowest excited slates is expected to occur for compounds with N-alkyl-(or N-cycloalkyl-) groups of high electron donating character, and is expected to increase as the solvent polarity decreases. This results in an efficient and temperature-dependent internal conversion to the ground state (pseudo-Jahn-Teller effect or proximity effect). The temperature-independent component of intersystem crossing may be identified with a barrierless transition from the lowest singlet to a lower-lying 3( ππ* ) triplet state, while the thermally activated isc process is probably a transition to a higher 3( nπ* ) triplet state.

Original languageEnglish
Pages (from-to)225-231
Number of pages7
JournalJournal of Photochemistry and Photobiology A: Chemistry
Volume113
Issue number3
DOIs
Publication statusPublished - Mar 15 1998

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Keywords

  • Aromatic dicarboxitnides
  • N-alkyl- and N-cycloalkyl-substituted 1,2-naphthalimides
  • Photophysics

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Physics and Astronomy(all)

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